The invention relates to the field of intravascular delivery systems, and more particularly to dilatation balloon catheters.
In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guide wire, positioned within an inner lumen of an dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient""s coronary artery until the distal end of the guide wire crosses a lesion to be dilated. Then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient""s coronary anatomy, over the previously introduced guide wire, until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with liquid one or more times to a predetermined size at relatively high pressures (e.g. greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion.
In the design of catheter balloons, balloon characteristics such as strength, flexibility and compliance must be tailored to provide optimal performance for a particular application. An important consideration in the design of the dilatation catheter assemblies is the flexibility of the distal tip of the catheter at the distal end of the balloon while maintaining the strength of the bond between the catheter and the balloon material. This flexibility affects the ability of the catheter for negotiating through the patient""s vasculature without causing injury thereto.
Therefore, what has been needed is a low profile balloon catheter with a flexible distal end while maintaining the integrity of the bond between the catheter and the balloon. The present invention satisfies these and other needs.
The invention is directed to an intravascular balloon catheter and a method for making the same. The catheter includes an elongated shaft having proximal and distal ends, an inflation lumen extending therein and a guidewire receiving lumen extending through at least a distal portion of the elongated shaft, and an inflatable balloon disposed on a distal shaft section. The distal shaft section of the catheter has a distal end, a port in the distal end. At least a part of the guidewire receiving lumen extends within the distal shaft section to the port in the distal end. At least part of the inflation lumen extends within the distal shaft section to a location proximal to the distal end of the distal shaft section. A distal portion of the guidewire receiving lumen has different hardness along a length thereof. In one embodiment, the distal portion of the guidewire receiving lumen is formed from two different sections. In an embodiment, the distal section of the two sections is softer than the proximal section. The two sections can be formed of similar material with different stiffness values or alternatively of different materials.
In one embodiment, the balloon has proximal and distal ends, proximal and distal tapered regions and an intermediate region longitudinally disposed therebetween. The proximal and distal regions each has a first end adjacent the intermediate region and a second end opposite the first end. A balloon distal shaft is disposed between the balloon distal tapered region second end and the balloon distal end. At least a portion of the balloon distal shaft sealingly extends over at least a portion of the two different sections forming the distal portion of the guidewire lumen and forms a distal shaft overlap. In one embodiment, the distal shaft overlap has a longitudinal dimension greater than the longitudinal dimension of the balloon distal tapered region, as measured along a catheter longitudinal axis.
In a method for making an intravascular balloon catheter, an elongated shaft is provided having proximal and distal ends, an inflation lumen extending therein and a guidewire receiving lumen extending through at least a distal portion of the elongated shaft to a shaft distal end; and an inflatable balloon on a distal shaft section of the elongated shaft as described above. A tubular member is provided having proximal and distal ends and formed of a material softer than a material forming the distal portion of the catheter shaft guidewire receiving lumen. The soft tubular member has at least one longitudinal incision along the tubular member extending from the tubular member proximal end to a point proximal to the tubular member proximal end. The proximal end of the tubular member is extended over the distal end of the catheter distal shaft section forming a distal shaft overlap, with a distance between two surfaces on two sides of the at least one incision increasing in the proximal direction to form a wedge. A mandrel is inserted into the catheter shaft guidewire receiving lumen and extends distally to a point proximal to the tubular member proximal end. The balloon distal shaft is radially disposed over the distal shaft overlap. A protective sleeve is disposed over the distal shaft overlap and energy to produce sufficient heat to melt the materials in the distal shaft overlap is directed onto the distal shaft overlap area to effect a seal in the distal shaft overlap area. The protective sleeve is thereafter removed.
The seal of the overlap area may be first formed between the proximal portion of the tubular member and the distal portion of the shaft guidewire lumen before the balloon distal shaft is disposed over that area with the seal between the balloon distal shaft and the overlap area being formed in a subsequent sealing step. In the alternative, the seal may be accomplished in a single sealing step between the proximal portion of the tubular member, the distal portion of the shaft guidewire lumen, and the balloon distal shaft.